1. Field of the Invention
This invention relates to a mechanism for mechanically excavating a tunnel or a blind hole upwardly from an underground location.
2. Description of the Prior Art
It is old to mechanically bore a relatively large diameter blind hole or a tunnel upwardly through an earth formation from an underground location. Rotary drilling machines for doing this are disclosed by Stoces, Bohuslav, D.Sc., Introduction to Mining, Vol. II, page 191, London: Lange, Maxwell & Springer Ltd.; and by U.S. Pat. Nos. 2,979,320 and 3,114,425. A disadvantage of these machines is that they all utilize a rotating drill stem which by necessity includes stabilizer sections of substantial size. To add a stabilizer section it is necessary to disassemble the mechanism used for collecting rock chips in order to make room for the stabilizer section. During these periods the workmen handling the drill stem sections are exposed to the hazards of an open raise. Also, the stabilizers drag against the bore wall as they rotate, increasing the torque requirements of the rotary drive mechanism. Further, it is never possible to bore a perfectly straight hole. The drill stem is always slightly curved despite the presence of stabilizers. As a result, the drill stem wobbles during rotation and the drill stem material is alternately subjected to tension and compression forces severely fatiguing such materials. Also, in such machines the mechanism for rotating the drill pipe must be advanced and retracted axially of tunnel. The apparatus required for doing this adds size to the underground machine.
Another type of machine for boring upwardly from an underground location is shown by U.S. Pat. No. 2,864,600. Such machine is supported by "gripper" mechanisms which make tight engagement with the tunnel wall rather than by drill pipe. A disadvantage of this type of system is that the gripper mechanisms require ideal ground conditions to be dependable and ideal ground conditions are not always present. U.S. Pat. No. 3,354,969 discloses a similar machine which includes an in hole power tunneler which is driven forwardly by powered drive wheels. This type of machine also requires ideal ground conditions.
U.S. Pat. No. 3,604,754 discloses an overhead boring machine of a type which utilizes both a gripper mechanism for engaging the bore wall and a sectional support column which is erected in the hole below the boring machine. In the system of this patent, the mined material or cuttings are delivered into the hollow interior of the support column. As a result, the machine at the underground site is quite complex because it requires a means for handling the column sections and advancing the column upwardly which must be constructed and positioned to not interfere with the discharge of the mined material out from the support pipe.
U.S. Pat. No. 3,840,272 discloses an overhead tunneling apparatus comprising a power tunneler which is supported from below by a non-rotating sectional support column. The sectional support column comprises a tubular center portion and a plurality of radially extending stabilizer fins which brace the support column against bending. The tunneler delivers the mined material into the space between a pair of such stabilizer fins through which space the material falls to a hopper mechanism below. The tunneler and the support column are advanced upwardly by a central thrust ram which also doubles as a support column loader. The support column is moved upwardly through a sealed opening in the bottom of the hopper and the column sections are added to and removed from the column in the space below such hopper.
U.S. Pat. No. 3,840,272 is owned by the assignee of this invention.